Have I a duff battery

[macafee2]

I took the battery off the car and put it on charge for a few days in the garage.
As soon as I took it off charge I measured the voltage and it was 12.8v, another battery that had been off charge for about a week measured 13.2v.

The above was about 3 or 4 days ago, I have just measured the suspected duff battery again and it is 12.57v. Not a lot of drop but as it was 12.8 when it came off charge I am suspecting it is duff.

Your thoughts please. If you too think it may be duff I will take it back and the shop can try a drop test.

macafee2

[MSS]

I wouldn't say the voltage you have measured necessarily indicates a duff battery.

I would put a mild load on the battery for a while and recheck the voltage. An old 55W 12V headlamp bulb consumes nearly 5Amps and makes a good test load.

[macafee2]

Originally Posted by MSS

I wouldn't say the voltage you have measured necessarily indicates a duff battery.

I would put a mild load on the battery for a while and recheck the voltage. An old 55W 12V headlamp bulb consumes nearly 5Amps and makes a good test load.

At say 2 minutes, what would I expect to see voltage wise?

macafee2

[MSS]

I would put the bulb on for 30 minutes. This will remove approximately 2.5Ah of charge from the battery which will have a capacity of around 70Ah for a 096 type when new.

You should get at least 12.5V which would indicate that the battery is at >90% fully charged.

If it drops to less than 12.5V, the battery is not as healthy as it should be.

[MSS]

What was the measurement or conclusion in the end?

[macafee2]

Originally Posted by MSS

What was the measurement or conclusion in the end?

Result, undecided about the battery. The voltage seemed not to drop any further, always staying above 12v. I am wondering if the fault is on the car. I kept a headlight bulb connected for well over an hour as suggested but the voltage stayed above 12.
I have just taken the battery off charge and it is showing 13.04v.

macafee2